The present invention relates to an optical integrated module created with hybrid photonic integration technology, and in particular relates to an optical integrated nodule configured by disposing an optical waveguide device between an input optical waveguide and an output optical waveguide.
As communication demand shifts from low speed service lead by telephones to broadband digital multimedia service, development of an optical ATM switching equipment having a high speed and high throughput for efficiently multiplexing whole these communication services and an optical switch having a high speed and excellent expandability as mainstay thereof is desired. Among all, a distribution selective optical switch configured by combining a one-input one-output high speed optical gate device and an optical multiplexer-demultiplexer device together is controlled easily, and therefore application for such use is being studied. In order to realize such an optical switch network, excellent crosstalk suppressing performance for satisfying scalability, high speed switching performance, and simple control system appropriate for speeding-up is required. Therefore, as this high speed optical gate, an optical gate device (SOAG) using semiconductor optical-amplifier (SOA) which has extremely high ON/OFF performance around 40 dB to 70 dB and can compensate loss of the optical multiplexer-demultiplexer device, and can be expected to respond at high speed of the order of nanosecond (nsec) is catching attention. In addition, in such a system that a number of such optical devices are used, costs as well as implementation load that these occupy the whole system cannot be ignored. Therefore, expectation toward a photonic integrated circuit (Photonic IC: PIC) which brings a plurality of optical devices into monosilic integration on one substrate and realizes a particular function and a photonic/electric integrated module that brings periphery electronic circuit devices, etc. for driving optical devices into integral integration is heightening. In particular, a hybrid optical integrated module in which a semiconductor optical device is implemented on an optical waveguide platform is expected as photonic integration technology that is closest to practical use from a point of view of its productivity, etc.
FIG. 10 is a plan block diagram showing an example thereof, in which an optical waveguide device 101 such as SOAG, having an optical waveguide 102 linked with the above described respective optical waveguides 104 and 105 are mounted on an optical waveguide platform 103 on which an input optical waveguide 104 and an output optical waveguide 105. In this hybrid photonic integrated device, the input optical signal 107 emitted into the input optical waveguide 104 is wave-guided through the input optical waveguide 104 and inputted to the optical waveguide device 101, and after being wave-guided through the optical waveguide 102, is wave-guided through the output optical waveguide 105 and is outputted as a core optical signal 108.
In the case where the optical integrated module on which the above described SOAG is mounted by application of hybrid photonic integration technology, in order to compensate a coupling loss due to relatively large optical waveguide discontinuity as between the input optical waveguide 104 and the optical waveguide 102 of the optical waveguide device 101 or between the optical waveguide 102 and the output optical waveguide 105, or a branching loss of the optical multiplexer-demultiplexer device, SOAG itself is required to have a large optical signal gain. Thus, measures to control residual facet reflection as much as possible is required to be taken, and therefore, angled facet structure in which the optical waveguide is bent in the vicinity of the light incident and emission facet obliquely toward this facet, or alternatively a window structure that discontinues the active stripe (active layer) immediately in front of the facet, etc. are proposed. For example, in FIG. 11, taken is such a configuration that toward the incident direction of the input optical signal 117 as well as the emitting direction of the output optical signal 118, the input optical waveguides 114 as well as the output optical waveguides 115 are inclined at a required angle and following this, portions connected with at least the input optical waveguides 114 and the output optical waveguides 115 in the optical waveguides 112 provided in the optical waveguide device 111.
However, in the hybrid optical integrated module shown in these FIG. 10 and FIG. 11, the optical signals to be emitted into the optical waveguide devices 101 and 111 subject to wave-guiding through the input optical waveguides 104 and 114 become unguided optical signal component which do not attribute to optical coupling in majority thereof in comparatively major discontinuity of optical waveguide between the input optical waveguide and the optical wave-guide device. This unguided optical signal component is brought into coupling again in the region of discontinuity of the optical waveguide in the optical waveguide devices 101 and 111 and the output optical waveguides 105 and 115, and this remarkably deteriorates overall ON/OFF performance toward optical signal of the optical gate device module. That is, majority of the unguided optical signals at the light incident side of the optical waveguide devices 101 and 111 are caused to go straight forward subject to gradual diversion like a beam in the substrate of the optical waveguide device 101 and 111 to reach the facet of the optical waveguide at the emitting side in the opposite side. Thus, the unguided optical signal(s) is (are) coupled into the output optical waveguides 105 and 115 existing in the vicinity thereof at a certain rate. This phenomenon becomes a cause to deteriorate the optical characteristics of the optical integrated module, in particular the ON/OFF characteristics of the optical signal in the optical gate device module such as, SOAG. Such an ON/OFF introduces coherent cross talk (beat noise) in optical signals and remarkably spoil the characteristics of the optical modules.
Particularly in case of an optical waveguide array device, such problems may be structurally caused by the fact that the emitting position of the unguided optical signals to be extremely closer to the emitting optical waveguide of another channel. For example, as shown in FIG. 12, in the case where the angled facet (angled facet) of the output optical waveguide 125 is formed in parallel along the angled facet of the input optical waveguide 124, since actually almost all of them is formed in point symmetry due to convenience in manufacturing, as a consequence, the propagation axis of the unguided optical signal (unguided signal) between the input optical waveguide 124 and the optical waveguide device 121 corresponds with an angle which is most apt to get coupled with the output optical waveguide 125. This introduces remarkable deterioration in inter-channel crosstalk suppressing characteristics.
In order to control such leakage of unguided optical signals, such measures that improve coupling loss so as to control occurrence of unguided optical signals themselves are first necessary. However, it is essentially impossibly to make coupling loss into zero in a hybrid optical integrated module, and a new device indeed for not coupling the unguided optical signal component as mulch as possible will rather become more important. However, it is the current state that none that can tolerate for practical use as a method to remove such unguided optical signal component effectively has been realized yet.
An object of the present invention is to provide an optical integrated module that has enabled to get rid of influence that the unguided optical signal given rise to due to discontinuity of optical waveguide essentially inevitable in hybrid photonic integration affects optical switching performance.
The present invention is an optical integrated module comprising an optical waveguide platform 133 on which an input optical waveguide 134 and an output optical waveguide 135 have been respectively formed and an optical waveguide device 131 which is mounted on the above described optical waveguide platform 131 between the above described input optical waveguide 134 and the output optical waveguide 135, and moreover is brought into optical coupling with the above described input optical waveguide 134 and the output optical waveguide 135, and is characterized in that the above described input optical waveguide 134 and the output optical waveguide 135, and the optical waveguide 132 of the above described optical waveguide device 131 which is brought into optical coupling with these optical waveguides have been bent in the region of these optical couplings respectively toward the same side with respect to a straight line oriented in the direction of optical waveguiding of the above described optical waveguide platform 133. In more particular, characteristics are that the above described input optical waveguide 134, the output optical waveguide 135 and the optical waveguide device 131 are disposed in such a positional relationship that a certain limited gaps are provided between the above described input optical waveguide 134 and the above described optical waveguide device 131, and between the above described output optical waveguide 135 and the above described optical waveguide device 131 respectively so that discontinued portions of optical waveguides are formed between them, and moreover the above described input optical waveguide 134, the optical waveguide 132 of the optical waveguide device 131 and the output optical waveguide 135 respectively comprise portions which have been respectively bent at a gentle curvature to such an extent that radiation of optical signals to be guided can be sufficiently ignored, and moreover each of the above described input optical waveguide 134, the output optical waveguide 135, and the optical waveguide 132 have been bent in the same direction in the vicinity of the above described discontinuity of the optical waveguide toward a straight line in the longitudinal direction of the above described optical waveguide platform 133 to comprise angled facet structure.
In the optical integrated module according to the present invention, the optical waveguide 132 on both incident and emission both facets of the optical waveguide device 131 is formed so as to get bent toward the same side along the straight line in the longitudinal direction of the optical waveguide platform 133, and the input optical waveguide 134 and the output optical waveguide 135 of the optical waveguide platform 133 are also formed so as to get bent toward the same direction along the bending of the above described optical waveguide 132, and thereby the direction of the longitudinal axis of the output optical waveguide 135 does not correspond with the wave-guiding axis of the unguided optical signal in the input optical signal 137 to be given rise to between the input optical waveguide 134 and the optical waveguide device 131, and the unguided optical signal intersects at such a deep angle as approximately twice the set angle of angled optical waveguide toward the output optical waveguide 135. Therefore, the unguided optical signal is emitted into the output optical waveguide 135 at a deep angle exceeding an effective aperture for the output optical waveguide 135 so that the crosstalk component 139 is controlled to be guided to the output optical waveguide 135. Consequently, it becomes possible that only optical coupling efficiency for unguided optical signal is selectively and extremely effectively controlled while deterioration in coupling efficiency for the optical signal is suppressed to be as small as possible.